Hello! :)
This is my build of Gangplank, I know that is a lil bit expensive but I'm sure that if you follow the correct steps you can own your enemys by critick strikes with your gun!
This build works great on 5v5 and 3v3, I use to follow it always (in rank games too).

Well, this runes are similar to tryndamere's runes. I use to pick a high critical damage beacause in the game you can pick only infinity edge that incrase only 50% your critical damage, so with our runes we will have 30% more and 10% from masteries, so that makes 290% damage! (2.9*458 = 1328.2 damage per atack!) and if you use Q this will add 150 to the atack, that means, 2.9*608= 1800... :DDDDDDD With one hit you can take down a normal DPS or AP champ (maybe 2 xD)

Well, we are DPS critick champion so we need atack! That's why my masteries goes there :P !
If you read a lil bit what this masteries reward you will found the most important of them, 10% more to your critical damage, and critical strike.
Our game is only the critick strike and critick damage, so we have to incrase it.

The game start, and we have 475, buy a critick chance and 2 pots! This is the best start that you can do, so you have a lil bit more chance to hit your critick. After that we have to incrase atack speed and critical strike = Zeal! :). I use to take the berserker boot's so I incrase my atack speed (DPS).
Then we need to pick the Phantom Dancer's cuz we get more critical strike and speed. After buy it we should save money to take more critical chance, then we buy bf sword to incrase damage, and infinity edge. There is were our game start to rush :D.
Next item's can be changed but I use to pick them, life steal, atack dmg, atack dmg+speed, armor penetration.
Some of my friends pick another dancers and maybe life steal (Stark's Fervor).
But really take them in this order is important.

"Q" There is our all game. We pick 100% of our atack damage+some dmg by the skill. The critical shot's will be incrased so much with this skill.
At level 2 I pick "W" to get some life and also helps you to run from stun's or other ultimates.
Level 3 have to be Q for sure, but at level 4 you can choose, E or W that's on your own desisicion.
At level 6 (our ulty) can help alot in team fight!

Ignite and Exhaust. Ignite for the runner who want to escape and exhaust to avoid runing or to escape. You can change them for teleport and something else but there is in your own way.

Hit from range and wait your cool down. Try to hit the enemy with Q, if you have been stuned or slowed, you can drink your W to run. This skill will save you in a lot of situations. For example, you fight vs veigar, he stun's you and use his meteorite... drink and run away to turret or teammate to bring it on teamfight.
You can look for easy kill with your ulty, but i prefer to save it for defend turrets or teamfight.
If a tank have thornmail only hit him with Q, this will avoid to take your huge damage to yourself.